The present invention concerns a device for controlling the flow of intake and exhaust gas in an internal combustion engine.
The internal combustion engine of an automobile comprises a plurality of cylinders each forming combustion chamber for burning air/fuel mixture to produce a mechanical energy, which reciprocates a piston to produce a torque delivered to the drive shaft by means of a crank mechanism. Referring to FIG. 10, there is schematically shown an intake and exhaust valve system provided in a cylinder head 100 whose lower middle part forms a combustion chamber 102 per cylinder. Respectively provided in both sides of the combustion chamber 102 are an intake port 104 for taking in a fresh air/fuel mixture and an exhaust port 106 for exhausting the burnt gases, which are normally closed respectively by means of an intake valve 108 and an exhaust valve 110 pushed by valve springs 112 and 114. When opening the intake or exhaust port 104 or 106, a locker arm 126 or 128 pivots on a shaft 116 or 118 with one end connected to the stem of the intake or exhaust valve 108 or 110 and with the other end moved by the cam surface 122 or 124 of a cam mounted on a cam shaft 120.
The intake stroke of the engine opens the intake valve. After the compression and explosion stroke is made with the intake and exhaust valves closed, the exhaust stroke opens the exhaust valve. Generally, it is a common practice to arrange an overlap interval between the final stage of the exhaust stroke and the beginning stage of the intake stroke, during which the intake and exhaust valves simultaneously maintain the opening state in order to improve the intake and exhaust efficiency, as shown in FIG. 11. However, in this case, because the fresh air/fuel mixture and the exhaust gas exist together in the combustion chamber during the overlap interval, some of the intake fresh air/fuel mixture is discharged through the exhaust port by means of the inertia of the exhaust gases and some of the exhaust gases flows into the intake port, thus resulting in the degradation of the output efficiency of the engine together with the discharge of some of the unburnt gases.
Means to resolve this problem is proposed in the Japanese Utility Model Publication No. 93-9456 entitled as "Gas Supplying Control For A Two Cycle Engine". This discloses a moveable mask plate that is mounted between the intake valve and the valve seat in the intake port to close the exhaust valve opening. The moveable mask plate is to close the exhaust valve opening in the initial stage of the opening of the intake valve, and to open the opening of the intake valve. This prevents the exhaust gases from flowing backwards, but not the intake air/fuel mixture from being discharged via the exhaust port. Moreover, the device may be employed only in the two cycle engine. In addition, the moveable mask plate is operated by the rocker arm, and therefore a separate cam is required to operate the exhaust valve.